Metal components, such as, for example, the blades or other components of a turbo-machine, in particular a turbine or compressor, may be subject to high stresses due to oxidation and/or corrosion and/or erosion and/or abrasion. In particular in turbine blades, these stresses may result locally in losses or abrasion of material at the surface of the blades, causing damaged areas, in particular in the form of relatively large recesses or holes, to form. Because of high prices for such blades, efforts are made to repair these damaged areas in the blades, in order to restore on the one hand their strength and on the other hand their flow quality. One possibility for repairing the damaged areas or the component consists of filling the damaged areas by using a high temperature soldering process. In a conventional process, a standard metal solder is used for the high-temperature soldering, which metal solder wets a metallic surface and then forms a diffusion bond with the metallic surface during soldering. To fill relatively large damaged areas, so-called xe2x80x9cwide gapxe2x80x9d solder is used. These are metal solders mixed with metal filler, whereby this metal filler preferably has similar properties as the metal of the metal component.
In particular as a result of the oxidative and corrosive stress on a metal component, non-metallic reaction products, such as, for example, oxides or nitrides, may form at the damaged areas. Since a standard metal solder is unable to wet non-metallic surfaces and is also unable to form a diffusion bond with them, these non-metallic reaction products are cleaned from the damaged areas to be filled, for example by grinding or sandblasting. It was found, however, that the fillings applied by a conventional high-temperature soldering process, in particular in the case of highly stressed turbine blades, in some cases does not possess satisfactory durability, so that even after a relatively short service life damaged areas may reoccur in the repaired area.
U.S. Pat. No. 5,334,344 discloses a method for soldering a ceramic part, a monocrystal, and a metal part to a monocrystal, or of a ceramic part to a monocrystal, or of a monocrystal to a metal part, whereby an active solder is used to produce the soldering bond. xe2x80x9cActive solderxe2x80x9d means an alloy that contains at least one element, such as, for example, titanium, that has an affinity for non-metals, for example, oxygen, nitrogen, so that no flux is necessary during the soldering process. An active solder therefore possesses the property of being able to wet both metallic and non-metallic surfaces and being able to form a reaction bond during soldering with a non-metallic surface, and a diffusion bond during soldering with a metallic surface.
The invention at hand has the objective of designing a method of the initially mentioned type in such a way that a repair performed according to this method has an improved durability.
According to the invention, this objective is realized in a method of the initially mentioned type in that an active solder is used in a high-temperature soldering process employed to fill the damaged areas.
In one aspect of the invention, there is provided a method for repairing a superficial damaged area in a metal component formed as a result of a loss of material. In a first embodiment, the method fills the damaged area by way of a high-temperature soldering process using an active solder.
In another embodiment, the method mixes a metal filler with the active solder. In an additional embodiment, the active solder is applied as a layer to the damaged area, and a conventional metal solder is applied to the active solder layer. In a further embodiment, the a conventional metal solder is mixed with the active solder. In yet an additional embodiment, the active solder is formed at or in the damaged area by first applying an active metal and a conventional metal solder to the damaged area. In a still further embodiment, a metal filler is mixed with the metal solder.